1. Field of the Invention
The present invention relates to a MOS transistor and a method of fabricating the same and, more particularly, to a MOS transistor having a recessed channel region and a method of fabricating the same.
2. Description of Related Art
Semiconductor devices have widely employed discrete devices, such as field effect transistors (FETs), as switching devices. Generally, the operating speed of a transistor depends on an activation current supplied to a channel region formed between a source region and a drain region. Conventionally, a planar transistor may be prepared by forming a gate electrode and source and drain regions in a device forming region of a substrate, i.e., an active region. The conventional planar transistor includes a planar channel region interposed between the source and drain regions. An activation current of the planar transistor is proportional to the width of the active region and inversely proportional to a distance between the source and drain regions, i.e., a gate length. Thus, the gate length should be reduced to increase the activation current and the operating speed of a device. However, as the distance between the source and drain regions decreases, a short channel effect (SCE) may occur in the planar transistor.
In order to overcome the SCE, and also downscale the transistor, a transistor having a recessed channel region has been proposed. The recess-channel transistor has a greater effective channel length than that of a planar transistor. In other words, the recess-channel transistor can structurally improve problems caused by the SCE.
A method of fabricating a recess-channel transistor is disclosed by Lee in U.S. Patent Publication No. 2007/0004127 A1 entitled “Method of Fabricating a Transistor Having the Round Corner Recess Channel Structure.” A recess-channel MOS transistor disclosed by Lee has a greater effective channel length than that of a conventional planar transistor. However, relatively smaller current flows through the recess-channel MOS transistor disclosed by Lee compared to a planar transistor designed at the same threshold voltage. That is, the recess-channel transistor is inferior in current drivability with respect to the planar transistor.
What is needed is a transistor that has a greater effective channel length than a planar transistor, together with the relatively high current driveability of a planar transistor.